"We are now going for more and more surveillance devices. We have purchased a large number of hand-held thermal imagers so that troops could effectively check movement of people across the Indo-Bangla border," BSF Director General AK Mitra said.

The state-of-the-art hand-held thermal imagers were now only available with the army in Jammu and Kashmir.

Observing that the porous border is providing safe haven to the militant outfits of Northeast, Mitra said he had pushed for the fencing to be completed as early as possible along the 4096-kilometre-long Indo-Bangla border.

However, he said, even if the fencing was completed, it would not be possible to prevent infiltration in the entire region because of its difficult terrain.

"The terrain in the region is such that it would be impossible to effectively prevent infiltration in the entire area," he said.

Asked about dealing with the BDR which often resorts to indiscriminate firing in the frontier, he said the troops have been given clear-cut instructions to give a befitting reply if they are fired upon by the Bangladesh Rifles.

"My instructions are very clear. We will not fire the first shot. But if we are fired upon, then we will reply back and reply back very effectively," Mitra said.

Asked whether India's reply was not effective to the aggressive postures of the BDR in the past, Mitra, who took over the post from RS Mooshahary, refused to comment.

"I do not know what happened in the past. I do not want to comment on that," he said.

Mitra, who visited the country's eastern frontiers in March after assuming office in February, said his troops are also being provided patrolling vehicles to check trans-border movements of insurgents.

India had given a list of 172 insurgent camps to Bangladesh operating from that country last year.

Mitra, however, claimed that migration has come down as result of various measures taken by his force.